Apparatus for solid gas reaction

ABSTRACT

Continuous fluorination of carbon is carried out by employing an apparatus for contact reaction of solid powder and reactive gas which comprises a horizontal reactor having a trough provided with weirs (e.g. height: 1 to 6 mm., interval: 5 to 30 cm.) and a vibrating means for vibrating the trough, and in which carbon particles supplied continuously are transported on the trough in a form of thin layer by the vibration of the trough while continuing the reaction by contacting efficiently the carbon particles with a fluorine gas. The contact reaction is efficiently conducted without accumulating the reaction heat to produce the fluorinated carbon in high yields, and the process is useful for the mass production. The apparatus is also useful for various contact reaction of a solid powder and a reactive gas.

BACKGROUND OF THE INVENTION

The present invention relates to a process for the continuousfluorination of carbon, and more particularly to a process for preparinga fluorinated carbon such as poly(carbonmonofluoride) orpoly(dicarbonmonofluoride) by contact reaction of carbon with a fluorinegas. The present invention also relates to an apparatus for solid-gasreaction wherein the reaction of a solid and a gas is efficientlyconducted without accumulating the reaction heat.

Recently, a fluorinated carbon has been watched as a new industrialmaterial, and has been applied to various uses, for instance, as anactive material for primary cells of high energy density, as a solidlubricant contained in liquid lubricants, greases and coatingcompositions, and as a fluorinating agent. Therefore, the demand for thefluorinated carbon has increased and a process for the preparationthereof suited for the mass production has been desired.

Hitherto, there have been adopted a batch process in which the reactionis carried out by passing a fluorine gas diluted with an inert gasthrough carbon particles placed in a reactor without any forcedtransference and the reaction product is taken out from the reactorafter the completion of the reaction; and a continuous process in whichthe reaction is carried out by passing a fluorine gas diluted with aninert gas through carbon particles which are being transferred in arotary kiln.

However, the batch process has the defect that the production capacityper bed area of a reactor is low and the production efficiency is bad.When the reactor is charged with a large quantity of carbon particles inorder to raise the production efficiency, in other words, when thecarbon particles are put on a bed of the reactor in a thick layer, thereaction heat is remarkably accumulated, since the thermalconductivities of the starting carbon particles and the producedfluorinated carbon are low and the reaction heat is not efficientlyremoved. Therefore, the thermal control is conducted with difficultyduring the reaction, and as a result, degradation of the fluorinatedcarbon frequently takes place in the course of the reaction. When thecarbon particles are put on the bed in a thin layer, much labor and timeare required, thus lowering the production efficiency, though theaccumulation of the reaction heat is avoided. Also, in the batchprocess, the contact efficiency is very inferior.

The continuous process using a rotary kiln can eliminate the problem ofthe batch process in taking the particles in and out. However, the heatefficiency is bad, and the heat removal is also bad because of aneffective area of heat transfer being small. Moreover, uniform mixing ofthe particles is insufficient. The process also has the disadvantagesthat the reactor per a unit production amount is large and uselessspaces are many, and the structure of the reactor is complicated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for thecontinuous fluorination of carbon.

A further object of the invention is to provide a process for thecontinuous fluorination carbon suitable for the mass production.

Another object of the invention is to provide an apparatus for solid-gasreaction suitably employed for continuously fluorinating carbonparticles.

These and other objects of the invention will become apparent from thedescription hereinafter.

It has now been found that the above-mentioned objects can be attainedby continuously fluorinating carbon with a fluorine gas employing as areactor a vibrating transportation apparatus having a trough providedwith a plurality of weirs.

In accordance with the present invention, there is provided a processfor the continuous fluorination of carbon in a horizontal reactor, saidreactor having a trough provided with a plurality of weirs, carbon feedand exhaust ports in both end portions of the reactor and fluorine gasfeed and exhaust ports in both end portions of the reactor, whichcomprises the steps of:

(a) introducing continuously a carbon onto the trough through a carbonfeed port in one end portion of the reactor,

(b) introducing a fluorine gas or a mixture of fluorine gas and diluentcontinuously into the reactor through a fluorine gas feed port in oneend portion of the reactor,

(c) bringing the carbon into contact with the gas to react them at atemperature of 200° to 600° C., while transporting said carbon on thetrough in a stream of the gas with vibration, and

(d) removing the fluorinated carbon continuously through a carbonexhaust port in another end portion of the reactor.

The present invention also provides an apparatus for contact reaction ofa solid powder and a reactive gas, particularly suited for use in thecontinuous fluorination of carbon, which comprises

(a) a horizontal reactor composed of a trough and a cover, said troughhaving a plurality of weirs at intervals on the upper surface,

(b) a vibrating means for vibrating the trough,

(c) feed and exhaust ports for a solid powder in both end portions ofthe reactor, and

(d) feed and exhaust ports for a reactive gas in both end portions ofthe reactor.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a schematic section view of an apparatus forcontact reaction of a solid powder and a reactive gas showing anembodiment of the present invention.

DETAILED DESCRIPTION

In the process of the present invention, a vibrating transportationapparatus having a trough provided with weirs is employed as a reactorand the fluorination of carbon particles is carried out whiletransferring the particles in a form of thin layer with vibration, andthereby the following advantages are exhibited. Since the contact ofcarbon particles with a fluorine gas and the scattering of the reactionheat are effectively conducted and the reaction heat is sufficientlyremoved without accumulation, heat control in the reaction is easy.Also, since weirs are provided on the trough, the thickness of theparticle layer on the trough and the transportation amount can becontrolled, and also vortical mixing of the particles takes place beforethe weirs and it contributes to making the reaction conduct uniformly.The particles get over the weirs one after another and are glidinglytransported on the trough, and uniformly fluorinated carbon particlescan be continuously prepared without causing the lowering of the yielddue to degradation. Further, the structure of the reactor is simple, andthe reactor can be easily made small-sized or large-sized. It is alsopossible to easily control the transportation of the particles bychanging the amplitude of vibration or the angle of inclination of thetrough, and moreover abnormal reaction such as dust explosion due tovibration does not take place, since the transportation of the particlesis smooth and there is no plying of the particles. Thus, the process ofthe present invention is very suitable for the mass production offluorinated carbon, and is industrially very advantageous.

It is contrary to common sense to employ a vibrating transportationapparatus which has originally been developed for the purpose of masstransportation, as a reactor for the preparation of a fluorinated carbonwhich is slippery and is generally in the form of finely divided powderhard to transport. In fact, such a proposal has not yet been known. Thepresent inventors have succeeded in development of a process for thecontinuous fluorination of carbon which can unexpectedly produceremarkable effects as mentioned above on the basis of the speciality ofthe present reaction, by providing weirs on a trough of a vibratingtransportation apparatus.

When such a vibrating transportation apparatus having a trough providedwith weirs is employed, reaction of a solid powder and a gas can be veryefficiently conducted and the heat transfer can also be easilyconducted. Therefore, the above-mentioned particular vibratingtransportation apparatus is available for use in not only the continuousfluorination of carbon, but also a usual contact reaction of a solidpowder and a reactive gas. For instance, the apparatus may beeffectively employed in a chemical reaction of inorganic powders andhalogen gases or other reactive gases, e.g. reaction of iodine andfluorine gas, reaction of alumina and hydrogen fluoride gas and reactionof cobalt fluoride and fluorine gas, and in a chemical reaction orsurface treatment of polymer powders such as polytetrafluoroethylene,polyethylene and polystyrene with reactive gases such as fluorine gas.Thus, according to the present invention, there is provided an apparatusfor contact reaction of a solid powder and a reactive gas whichcomprises a horizontal reactor composed of a trough and a covertherefor, the trough having a plurality of weirs at intervals on theupper surface, a vibrating means for vibrating the trough, and two pairsof feed and exhaust ports for the powder and the reactive gas providedin both end portions of the reactor.

The apparatus of the present invention is applicable to various solidpowders such as inorganic materials and organic high polymers, andparticularly to those having a particle size of not more than 50μ.

A rotary vibrator and an electromagnetic vibrator may be employed as thevibrating means, and are selected depending on the shape of the solidpowder and the particle size. In general, when the particle size issmall, an electromagnetic vibrator is preferred.

The apparatus may further include a heater for heating the reactor and acooling means for keeping the vibrating means from superheating. Also,there may be attached to the inside of the cover for the trough aplurality of baffle boards projecting downward, and thereby thedirection of the stream of a reactive gas is changed so that thereactive gas is sufficiently brought into contact with a solid powder onthe trough.

The apparatus of the present invention shown generally at 29 will beexplained with reference to the accompanying drawing which is aschematic sectional view showing a preferred embodiment of theinvention. A reactor shown generally at 30 is formed by a trough 1 and aceiling or cover 2 so as to be sealed. Hopper 3 is connected to rotaryfeeder 3a for feeding a solid powder to reactor 30, and they are locatedabove cover 2. Rotary feeder 3a is connected to feed port 32 in theupper part of one end portion of reactor 30 through flexible hose 14.Vessel 4 for receiving the product is located at another end portion ofreactor 30, and is connected to exhaust port 34 through a flexible hose36. Feed port 5 for feeding a reactive gas is mounted in one end portionof cover 2, and exhaust port 6 for exhausting the gas is mounted inanother end portion of the cover 2. Trough 1 is provided with aplurality of weirs 8 projecting upward from upper (inner) surface 38 ofthe bottom wall 42 of trough 1 at intervals, and weirs 8 may projectupward with a slight gradient against the travelling direction of thepowder. Cover 2 is provided with a plurality of baffle boards 7 atintervals to project downward into trough 1. Heater 9 for heatingreactor 30 and a cooling means 10 for preventing the heating ofvibrating means 13 are positioned outside and under trough 1. Vibratingmeans 13 for vibrating reactor 30 has electromagnets 12 which act as thevibration source, and the trough 1 supported by plate springs 11 isvibrated by electromagnets 12. The powder supplied from feeder 3a andheated by heater 9 is gradually transferred toward product vessel 4,while coming into contact, preferably counter current contact, with areactive gas and continuing the reaction. The product in vessel 4 isrecovered through rotary valve 16 and discharge line 40. Thermometer 15is placed on the trough 1.

In case of vibrating means of a rotary vibrator type, the trough isvibrated by the exciting force of unbalanced weights attached to bothends of a rotor axis of a motor.

Weirs 8 are mounted on trough 1 at desired intervals, usually atintervals of 5 to 30 cm. The height of weirs 8 is from 1 to 6 mm.,preferably 2 to 4 mm. When the height of weirs 8 is less than 1 mm., thelayer of powder on the trough becomes too thin and it is necessary tomake the area of the reactor large. On the other hand, when the heightof the weir is more than 6 mm., transfer and uniform mixing of thepowder become difficult and overheating may occur.

Trough 1 may be horizontal or it may be slightly inclined. The degree ofinclination is selected from -4° to +4°, preferably +2° to 0°, in which(+) means the inclination that the powder runs down, (-) means theinclination that the powder runs up and 0° means that the trough ishorizontal. When the degree of inclination is more than -4°, the powderdoes not move forward, and when the degree of inclination is more than+4°, the powder slides on the trough in avalanche and the transportationcontrol becomes difficult.

The contact reaction apparatus of the present invention has thefollowing advantages.

1. A solid powder and reactive gas are effectively utilized and theproduction capacity per bed area is remarkably increased, since thevibrating trough having weirs is employed, and if desired, the baffleboards are attached to the cover, so that good contact of powder andreactive gas results, thereby permitting the process to be conducted ina continuous manner.

2. The powder moves smoothly on the trough. Also, thickness of thepowder layer and the transportation of the powder are easily controlledby changing the height of the weirs, the amplitude of vibration of thetrough or the angle of inclination of the trough.

3. Uniform contact and reaction take place, since the vortical mixing ofthe powder takes place before the weirs and the powder is sufficientlyadmixed.

4. Heat transfer is good, and heat control is easy. Heating of thepowder and removal of the reaction heat are effectively conducted.

5. The reaction is conducted efficiently. When a reactive gas is causedto flow countercurrently through the reactor, the reaction efficiency isfurther increased, since fresh powder contacts lower concentration ofreactive gas without causing rapid reaction and powder that has beenpartially reacted with the reactive gas is brought into contact with ahigher concentration of the reactive gas.

6. The structure of the apparatus is simple, and the apparatus is easilymade either in a small size or in a large size.

The process for the continuous fluorination of carbon of the presentinvention is practiced by employing the contact reaction apparatus asmentioned above. Since fluorine gas is very reactive, a nickel alloysuch as Monel metal made by International Nickel Co. and nickel arepreferred as the material of the reactor. The process of the presentinvention will be explained with reference to the accompanying drawing.

A carbon which is the starting material, in hopper 3 is supplied throughthe rotary feeder 3a into reactor 30, and is transported on the trough 1in the direction of the product vessel 4. A fluorine gas is preferablycaused to flow countercurrently to the carbon. The carbon on the trough1 countercurrently contacts a fluorine gas supplied through fluorine gasfeed port 5 to react therewith. When electromagnets 12 are excited by apulsating current from a regulator of vibrating means 13, trough 1 issuddenly drawn downward by electromagnet 12. Since its speed is large,the carbon floats and falls forward onto trough 1 by the gravity. In thenext instant, trough 1 is repelled forward and upward by the force ofplate springs 11 so as to further move the carbon forward. At weirs 8projecting upward from the bottom of trough 1, the carbon is mixed intoa vortex and comes into contact with the fluorine gas, so the carbonslidingly, smoothly moves on the trough 1 while continuing the reaction.The reaction product is collected into vessel 4 through flexible hose36. The fluorine gas supplied from feed port 5 is passed through reactor30 and is exhausted from exhaust port 6. The fluorine gas passingthrough the reactor runs against baffle boards 7 projecting down fromthe cover 2, and its flow direction is changed so as to effectivelycontact the carbon in trough 1. A plurality of the apparatuses may beconnected, as occasion demands, and the product obtained in thepreceding apparatus may be further supplied to the next apparatus, whenthe apparatuses are connected in series.

The vibration may be conducted continuously or intermittently; duringthe reaction, the trough is always vibrated or vibration and stoppage ofthe trough is repeated. The vibrating transportation of a solid powderis desirably carried out under the following conditions. The number ofvibrations of the trough is usually selected from 1,800 to 3,600 perminute. Within this range, the powder can be smoothly transported on thetrough. The amplitude of vibration of the trough is selected from 0.1 to1 mm., preferably 0.1 to 0.4 mm. When the amplitude of vibration fallswithin the above range, the powder smoothly moves with the appearancethat as if it is stationary. When the amplitude of vibration is morethan 1 mm., the powder frequently flies.

The carbon employed in the process of the present invention is notlimited, and also may be either amorphous or crystalline carbon. Forexample, the carbon may be amorphous carbons such as carbon black, coke,petroleum coke, pitch coke and charcoal, and crystalline carbons such asnatural graphite and artificial graphite. The carbon may be employed invarious forms, for instance, in the form of powder, sphere, small blocksand small masses. In general, a finely divided powder having an averageparticle size of not more than 50μ is preferred.

In the process of the present invention, a fluorine gas prepared by theelectrolysis of a solution of KF.2HF electrolyte may be employed. Thefluorine gas so prepared may be employed as it is, or the gas from whichimpure hydrogen fluoride is removed may be employed. A commerciallyavailable fluorine gas charged in a bomb may also be employed in theprocess of the invention. A fluorine gas may be employed alone, but itis generally employed in the form of a mixture with a diluent for thepurpose of the controlling the reaction because of high reactivity offluorine gas. The fluorine gas is usually diluted with an inert gas suchas nitrogen, argon, neon, helium, perfluorocarbons having 1 to 8 carbonatoms, air or carbon dioxide. The mixing ratio of the fluorine gas withthe inert gas may vary depending on the reaction conditions such as theflow rate of the gas mixture and the reaction temperature. In general,the fluorine gas and the inert gas are mixed so that the partialpressure of the fluorine gas in the gas mixture falls within the rangeof 0.5 to 0.01, preferably 0.4 to 0.1. When the partial pressure of thefluorine gas is more than 0.5, the reaction rate becomes so large thatthe reaction heat is hard to be removed and by-products such asperfluorocarbons are increased. When the partial pressure is less than0.01, the reaction rate becomes so slow that production efficiency isdecreased.

The reaction temperature is selected from 200° to 600° C., preferably200° to 500° C. Although the optimum reaction temperature generallyvaries within the above range depending on the kind of the carbon, therange of 200° to 450° C. is preferred for amorphous carbons and therange of 400° to 500° C. is preferred for crystalline carbons.

The degree of the fluorination may be suitably controlled according tothe process of the present invention. Therefore, the process of theinvention is also applicable to partial fluorination of carbon,especially to the fluorination of only the neighborhood of the surfaceof the carbon particles.

The process of the present invention is more particularly described andexplained by means of the following Examples. These Examples areintended to illustrate the invention and not to be construed to limitthe scope of the invention.

EXAMPLES 1 TO 6

Fluorination of carbon was carried out by employing a vibratingtransportation type reactor as shown in the accompanying drawing, inwhich the sizes of the trough 1 were 10 cm. wide and 80 cm. long, theweirs 8 having a height of 10 cm. were attached onto the trough atintervals of 10 cm., the baffle boards 7 having a height of 2 cm. wereattached to the cover 2 at intervals of 20 cm., panel heaters 9 werefixed to the under surface of the trough, and a jacket water cooler 10was provided between the trough and the electromagnets 12 of theelectromagnetic vibrators 13 (the number of vibrations: 60 Hz).

Petroleum coke carbon powder having a particle size of 1 to 38μ storedin the hopper 3 was continuously introduced into the reactor through therotary feeder 3a. After the carbon powder was sufficiently preheated,the reaction was started under the conditions shown in Table 1 bycontinuously introducing a fluorine gas diluted with nitrogen from thefeed port 5 to produce poly(carbonmonofluoride). The reaction productwas collected in the vessel 4, and the yield and the fluorine content ofthe product were determined.

The results are shown in Table 1.

EXAMPLES 7 AND 8

The procedures of the preceding Examples were repeated except that avibrating transportation type reactor having the trough of 10 cm. wideand 200 cm. long was employed.

The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Example No.        1   2   3   4   5   6   7   8                              __________________________________________________________________________    Reaction temperature (°C.)                                                                400 460 495 460 460 460 450 450                            Degree of inclination of trough                                                                  +2°                                                                        +2°                                                                        +2°                                                                        +2°                                                                        +2°                                                                        +2°                                                                        +2°                                                                        +2°                     Vibration condition of trough                                                 Amplitude of vibration (mm.)                                                                     0.2 0.3 0.2 0.4 0.2 0.2 0.1 0.2                            Continuous vibration                                                                             --  --  --  --  --  --  Con.                                                                              Con.                           Intermittent vibration                                                        Stoppage period (min.)                                                                           6   12  6   7   6   3   --  --                             Vibrating period (min.)                                                                          0.5 0.5 0.5 0.5 0.5 0.5 --  --                             Concentration of fluorine gas (vol. %)                                                           15.0                                                                              15.0                                                                              15.0                                                                              15.0                                                                              30.0                                                                              45.0                                                                              20.0                                                                              20.0                           Flow rate of fluorine gas (liter/min.)                                                           2.5 2.5 2.5 2.5 1.3 1.7 11.5                                                                              7.6                            Average reaction time (min.)                                                                     120 120 120 60  120 60  30  22                             Reaction product                                                              Yield (g./hr.)     45  46  46  85  40  68  400 460                            Fluorine content (wt. %)                                                                         40.0                                                                              58.2                                                                              61.5                                                                              35.0                                                                              61.5                                                                              61.6                                                                              48.0                                                                              27.8                           __________________________________________________________________________

EXAMPLE 9

Two hundred fifty grams of petroleum coke carbon powder having aparticle size of 1 to 38μ were repeatedly subjected to the fluorinationreaction in the same manner as in Example 1 except that the trough wasintermittently vibrated (stoppage period of vibration: 5.5 minutes,vibration period: 0.5 minute) with the amplitude of vibration of 0.3 mm.and the reaction was conducted at 385° C.

The results are shown in Table 2, in which data on column 1, 2, 4, 6 or8 of "Number of repetitions of reaction" are those obtained in the 1st,2nd, 4th, 6th or 8th reaction, respectively.

                  TABLE 2                                                         ______________________________________                                        Number of repetitions                                                         of reaction  1       2       4     6     8                                    ______________________________________                                        Average                                                                       transportation amount                                                         of powder (g./hr.)                                                                         71      65      70    70    73                                   Reaction time (hr.)                                                                        4.5     5.5     6.5   7.0   7.0                                  Fluorine content                                                              of product (wt. %)                                                                         25.5    36.0    50.7  57.0  61.4                                 Yield of product (g.)                                                                      320     359     456   494   518                                  ______________________________________                                    

EXAMPLE 10

Two hundred fifty grams of petroleum coke carbon powder having aparticle size of not more than 38μ were repeatedly subjected to thefluorination reaction in the same manner as in Example 1 except that thetrough was intermittently vibrated (stoppage period of vibration: 5.5minutes, vibration period: 0.5 minute) with the amplitude of vibrationof 0.3 mm. and the reaction was conducted at 450° C. by passing afluorine gas having a concentration of 10 vol. % at a flow rate of 3.8liters/min.

The results are shown in Table 3, in which data on column 1, 2, 3 or 4of "Number of repetitions of reaction" are those obtained in the 1st,2nd, 3rd or 4th reaction, respectively.

                  TABLE 3                                                         ______________________________________                                        Number of repetitions                                                         of reaction    1        2       3      4                                      ______________________________________                                        Average transportation                                                        amount of powder (g./hr.)                                                                    70       68      70     74                                     Reaction time (hr.)                                                                          4.5      5.5     6.5    7.0                                    Fluorine content                                                              of product (wt. %)                                                                           27.3     45.5    58.3   61.0                                   Yield of product (g.)                                                                        299      379     457    525                                    ______________________________________                                    

What we claim is:
 1. An apparatus for contact reaction of a solid powderand a reactive gas, said apparatus comprising:(a) a horizontal reactorhaving two end portions with a feed port for receiving a solid powderpositioned in one end portion, a discharge port for discharging productpositioned in the other end portion, a feed port for receiving reactivegas positioned in one end portion and a discharge port for dischargingsaid gas positioned in the other end portion, said horizontal reactorcomprising:(i) a trough comprising:(A) a bottom wall, (B) end walls, and(C) side walls, each wall having an inner surface and an outer surface,and (D) a cover having an inner surface and an outer surface; (ii) aplurality of weirs positioned at intervals on the inner surface of thebottom wall and projecting upward therefrom; and (iii) a plurality ofbaffle means positioned at intervals on the inner surface of the coverand projecting downward therefrom; and b) vibrating means for vibratingthe trough.
 2. The apparatus of claim 1, wherein the height of saidweirs is from 1 to 6 mm.
 3. The apparatus of claim 1, wherein saidtrough is provided with weirs at intervals of 5 to 30 cm.
 4. Theapparatus of claim 1, wherein said vibrating means is a rotary vibratoror an electromagnetic vibrator.
 5. The apparatus of claim 1, furthercomprising a heating means for heating the reactor.
 6. The apparatus ofclaim 1, further comprising a cooling means positioned between thetrough and the vibrating means.